Preparation And Multiferroic Properties Research Of BiFe_0.97Mn_0.03O₃-based/Magnetic Layer Composite Thin Films

The applications of Bi FeO₃ are limited owing to the large leakage current,weak multiferroic properties and other problems.Multi-ions doping has an positive effect on the reduction of leakage current and the improvement of ferroelectric properties,but it isn't a useful method for ferromagnetic properties.The ferromagnetic material can be introduced to solve this problem.However,the ferroelectricity deteriorates with the enhancement of ferromagnetism.In order to solve the problem of the incompatibility of ferromagnetism and ferroelectricity,the ions-doping is applied to the composite thin films.Meanwhile,the resistive switching effect exists in the composite thin films.But the relationship between ferroelectric polarization and resistive switching effect needs to be further discussed,this tunning study empowers practical significance of the design freedom of multi-function devices that based on BFO thin film.In this project,the chemical solution deposition method was employed to prepareBi_1-xPr_xFeMn_0.03O₃?BPr_xFMO?,Bi_0.85-yPr_0.15Dy_yFeMn_0.03O₃?BPDy_yFMO?,Bi_0.85-zPr_0.15RE_zFe_0.97Mn_0.03O₃/CuFe₂O₄?RE=Sr,Dy??BPRE_zFMO/Cu FO,RE=Sr,Dy?and Bi_0.96Sr_0.04Fe_0.98Co_0.02O₃/CoFe₂O₄?BSFCO/CFO?thin films.The influences of ions co-doping on the structure,microtopography,electrical and multiferroic properties,and the effects of magnetic layer on the multiferroic and resistive switching behavior of BFO thin film have been studied.The results are as follows:?1?The structure,morphology,electrical properties and multiferroic were characterized.The structure of thin film was transformed from R3c:H trigonal phase to P4 tetragonal phase which was induced by Pr doping.The formation of oxygen vacancy and Fe²⁺ion was suppressed,meanwhile,the grain refinement facilitates the increase of grain boundary resistance,causing the decrease of leakage current densities.The ferroelectric properties were optimized,the remanent polarization and polarization current of BRr_0.15FMO thin film are 91.3?C/cm² and 0.028 A,respectively.This film possesses good ferroelectric stability.?2?The effects of Dy doping on the srutcture,electrical properties and multiferroic were studied.Dy doping induces the further transformation of structure so as to increase the grain boundary resistance and decrease the leakage current density.The ferroelectric properties of BPDy_yFMO?y=0.04-0.07?were deteriorated,which the remanent polarization decreased from 91.3?C/cm² to22.2?C/cm².The appeared ferroelectric aging effect of thin films was attributed to the pinning effect at domain walls which caused by defect complexes.The ferromagnetic properties of BPDy_0.04FMO thin film improved to some extent at the same time and the saturation magnetization was 2.39 emu/cm³.?3?Researchs of structure and properties of BPRE_zFMO/CuFO?RE=Sr,Dy?composite thin films are made.The trigonal R3c:H structure of BFO was retained.The composite thin films show the better multiferroic properties,the remanent polarization of BPSFMO/CuFO is 84.3?C/cm²,and the remanent magnetization of 15.8 emu/cm³ is 23.6 times bigger than that of BFO?0.67emu/cm³?.Furthermore,the dielectric relaxation and the resistive switching effect appeared in the composite films simultaneously,and ions-doping weaks the resistive switching behavior.?4?In the BFSCO/CFO composite thin films,the effects of mismatch strain caused by lattice mismatch in the film on the structure of BSFCO layer.The occurred dielectric relaxation belongs to Maxwell-Wagner relaxation.The dielectric relaxation time decreases,which is attributed to the enhancive resistance and the depressed capacitance of the thicker BSFCO film.The composite films with thicker BSFCO layer show the improved ferroelectric properties,and the strong ferroelectric polarization switching decreases the potential barrier height in the p-n junction,this is beneficial to the exhibition of resistive switching behavior.